The invention relates to switching voltage converters such as voltage transformers or rectifiers in half bridge topology. The general working principle of such switching voltage converters is based on a primary voltage which is chopped preferably BY electronic switches to obtain a desired AC voltage. This AC voltage is then suitably processed in a transformer and/or filter and/or rectifier to obtain an output voltage in the desired form and with desired characteristics.
The prior art includes switching voltage converters principles which use PWM (pulse width modulation). Such devices are disclosed, by Tietze/Schenk, chapter 18 (ISBN 3-540-19475-4, 9th edition). In such converters a half bridge topology feeds a transformer. The locking time between the power switchxe2x80x94typically n-channel transistorsxe2x80x94in high and low conditions is varied to adjust the duty ratio of the chopped AC voltage. This results in a voltage or current of the desired characteristics at the output of the converter.
Mutually exclusive signals, also called one-hot signals, are defined here as two signals which are generated by the biasing of the pulse width modulator in a way that to prevent short circuits. In this technique, only one of the two switches is closed (is hot) at any given time.
There are also embodiments of converter principles in which the locking time between the two power switches of the half bridge is constant, as, for example, in the case of resonance converters. Resonance converters employ very high switching frequencies which reduces their switching power losses. They control the power to be transformed or its output voltage by varying the switching frequency. As a rule, this switching frequency is generated by a VCO (voltage controlled oscillator).
In prior-art embodiments, this VCO is at a quiescent potential. The switching signals generate by the VCO are transmitted via a suitable signal and potential separation to the power switches or their drivers. This arrangement is used mainly when the intermediate circuit voltage supply of the half bridge has a higher voltage than the associated oscillator circuit.
An example of the prior art is disclosed in DE 33 11 662, in which a circuit arrangement is used in an electromagnetic flowmeter. This circuit arrangement does not meet the requirements of the present invention, although it does introduce a half bridge arrangement with constant locking time.
Another example of the prior art is disclosed in Japanese patent JP 63253720, which introduces an arrangement in which the driver controls a half bridge consisting of an n-channel and a p-channel IGBT. This arrangement is provided with a reference potential of the gate driver which is not constant in time but equals the potential of the output voltage of the half bridge. By using an n-channel TOP switch and a p-channel BOT switch, both of which are jointly controlled by only one gate driver, a very short locking time and secure locking is achieved. The switching signal is transmitted to the driver via an optocoupler which takes over the task of signal or potential separation.
In the case of a resonance converter, comparatively high switching frequencies must be transmitted. For that reason, it is difficult and expensive to realize this signal or potential separation for the switching signal.
It is an object of the present invention to provide a switching voltage converter in a semi-bridge topology with constant locking time and low requirements in terms of switching technology for controlling the half bridge.
Briefly stated, the present invention provides a switching voltage converter in half bridge topology which includes a control circuit for achieving a constant locking time for two power switches to switch between a TOP position and BOT position. The TOP switch is realized by one or more parallel-switched n-channel transistors and the BOT switch 3 is realized by one or more parallel-switched p-channel transistors. Both of the power switches are controlled by a gate driver. The reference potential of the gate driver is at the potential of the output signal Uout of the half bridge. The driver is controlled by a switching-signal producing unit at the same reference potential as the driver 1, whereby unit and driver can be directly connected to each other.
According to an embodiment of the invention, there is provided a awitching voltage converter in half bridge topology with a constant locking time between the a TOP switch and BOT switch, comprising: a control device, the TOP switch being at least one parallel-switched n-channel transistor, the BOT switch being at least one parallel-switched p-channel transistor, a gate driver controlling the TOP switch and the BOT switch, whereby both power switches are controlled by a gate driver, and a reference and supply voltage potential of the gate driver and the switching unit being for controlling the gate driver are at a common potential.
In the inventive solution, in contrast to the prior art, the circuit unit (oscillator circuit) producing the switching signal is chosen to receive the same potential as the supply potential or reference potential for the driver circuit. Thus, the oscillator circuit has no fixed reference potential. Instead, the reference potential of the oscillator and the gate driver varies with the output signal of the half bridge. This permits connecting the oscillator directly to the driver. A signal or potential separation carrying the signal is not necessary. For the control, only a quasi-static, i.e. slowly changing, control signal must be transmitted to the oscillator circuit. Thus, the transmitting component is subject to considerably less stringent switching requirements compared with the requirements for transmitting a higher-frequency switching signal of the oscillator circuit.